This application claims the priority of German Application No. 196 34 368.2-52, filed Aug. 26, 1996, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a sensor system having a measuring element which exhibits a PT1-action. This group of so-called measuring elements of the first order includes, for example, temperature measuring elements, optical measuring elements, magnetic-field measuring elements, piezo-electric, inductive and capacitive measuring elements. The time response of this type of measuring element can be described by a first order differential equation with a time constant T.sub.1. See, for example, E. Schiessle, "Sensortechnik-und Me.beta.wertaufnahme" ("Sensor Technology and Measured-Value Sensing"), Vogel Publishers, 1992.
It is a characteristic of these measuring elements that their response to abrupt changes of the quantity to be measured is delayed by the time constant T.sub.1. As long as the value of the quantity to be measured changes linearly, a constant deviation remains between the measuring element output signal and the actual value of the sensed quantity; this difference corresponds to the product of the time constant T.sub.1 and the rise of the linear change. In the case of a dynamically changing quantity to be measured, this delayed action of the measuring element will therefore necessarily result in measuring value deviations. The use of a sensor system having a measuring element with a faster response time (that is, one with a lower time constant), can frequently not be implemented in practice or is at least connected with relatively high expenditures. One example of such a dynamically changing quantity is the engine oil temperature of a motor vehicle internal-combustion engine during a driving operation. Since control interventions into the engine operation, such as a cylinder cut-off as a function of the engine oil temperature, occur frequently, there is demand for a dynamic engine oil temperature sensing which is as accurate as possible.
The object of the invention is therefore to provide a sensor system of the initially mentioned type which uses a low-expenditure measuring element, and also supplies a relatively precise output signal also for a dynamically changing quantity to be measured.
This and other objects and advantages are achieved by the sensor system according to the invention, in which a measured-value analyzing unit connected behind the measuring element adds to the measured values supplied by the measuring element a correction value equal to the product of the measuring-element time constant (T.sub.1) and a sliding average value of the successively sensed measured change values. When a measuring element with a given time constant is used, the measured value which is corrected in this manner reflects the actual value of the quantity to be measured substantially better than the uncorrected raw measured value, especially if the quantity changes dynamically. In particular, the corrected measured value follows fast changes of the quantity to be measured more rapidly than the uncorrected measured value in that an averaged correction value, which takes into account the delayed action of the measuring element, is added to the uncorrected measured value which may be smoothed by averaging.
In an advantageous embodiment, the sensor system according to the invention can be used for sensing the engine oil temperature for internal-combustion engine systems of motor vehicles in which, for example, an engine control unit controls a cylinder cut-off as a function of the measured engine oil temperature value supplied by the sensor system. Advantageously, the engine control unit simultaneously forms the measured-value analysis unit of the sensor system which may optionally be implemented as a hardware or software component in the engine control unit.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.